Electromagnetic printer



Filed May 5l, 1956 Jan 15, 1962 l.. s. TRIMBLE ETAL 3,017,234

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ELECTROMAGNETIC PRINTER 14 Sheets-Sheet 14 Filed May 51, 1956 United States Patent G 3,017,234 ELECTROMAGNETIC PRINTER Lyne S. Trimble, North Hollywood, Michael J. Markakis, Playa Del Rey, Jerome L. Nishbail, Los Angeles, and Merton C. Leinberger, Inglewood, Calif., assignors to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Filed May 31, 1956, Ser. No. 588,450 16 Claims. (Cl. 346-74) This invention relates to an automatic electromagnetic printer and more particularly to a novel means and method of forming and recording electrical signals defining the shapes of designated symbols in response to coded information received from an outside source.

The increasing prominence of the large-scale coding devices, such as the electronic digital computer, in business applications and the continuing use thereof in scientific fields has placed large emphasis on the development of high speed printing equipment to convert the binary coded language generally employed in the digital computer into a printed, visible record of intelligible symbols, such as the alphabetic, numeric, etc. characters, represented by the code. For practicality in these applications, it is also desirable that the record be printed at a speed approaching that at which input is fed from the external source. Accordingly, it is highly desirable to be able to print directly in response to electrical signals representing the characters, i.e., to form the characters by magnetically recording signals defining the shape thereof. It is also very desirable that the different symbols or characters formed on the record in this manner be clearly distinguishable from each other and that confusion due to overlap of individual characters, intermingling of lines, meaningless spaces, etc. be eliminated by properly synchronizing and controlling the operations of the printer.

It is thus an object of this invention to provide a high speed electromagnetic printer possessing the aforesaid attributes to a degree which makes its use in an electronic computer data processing system devoted to billing, inventory control, etc., or in conjunction with equipment for plotting, teletyping, chart recording, etc., highly appropriate.

It is another object of this invention to provide a simple, reliable means for timing and directing the electrical signals so as to cause recording of the characters in the proper positions of the line of the medium.

It is a further object of this invention to provide a printer capable of accepting binary coded information and immediately recording the characters represented thereby to form successive lines of legible information on a medium useful for business purposes.

Another object of the invention resides in the provision of means to encode information received from the source equipment employing, in the preferred embodiment, a substitution code easily and rapidly changed by the operator of the printer without affecting the operation of the source equipment. A feature associated with this object is an unlimited number of character matrices (configurations), the number of characters contained in each matrix being a function of the number of different meaningful codes which can be set up as inputs to the printer. Thus the substitution code may arrange to affect the distribution of characters in the matrix and consequently the character actually printed in response to a code transmitted by the computer.

Other objects and many of the attendant advantages of the present invention will become readily apparent as the same become better understood by reference to the preferred embodiment detailed in the following description and accompanying drawings in which:

3,017,234 Patented Jan. 16, 1962 Nice FIG. 1 is a perspective view showing the overall arrangement of the components for performing the print- FIG. 4 is a cross-section of a portionof the drum .sur-- face showing the two types of projections provlded,

thereon.

FIG. 5 is a cross-sectional View of the drum of the recorder Showing the path of the magnetic field for recording.

FIG. 6 is a schematic diagram of the wave-shaping circuitry provided for generating timing signals.

FIG. 7 is a block diagram of the character counter.

of FIG. 2.

FIG. 8 is a block diagram of the sweep counter of FIG. 2.

FIGS. 9 to l2 are diagrams of hip-flops N1, P1, Q1; and M1 together with the logical equations defining they grid triggering networks therefor.

FIG. 13 is a graph of waveforms for explaining the operation of the N1 Hip-flop.

FIGS. 14 and 15 show the networks for generating'v propositions used by the character counter and print control circuit.

FIG. 16 shows the network of the transfer circuit of.

FIG. 2 which generates signal R.

FIG. 17 shows the network for generating the sum S,l used by the transfer circuit.

FIG. 18 is a schematicdiagram of the cathode ray` tube horizontal deflection circuitry.

FIG. 19 is a schematic diagram of the cathode ray tube' vertical defiection circuitry.

FIG. 20 is a plan View of a preferred form of mask indicating how the individual characters areas thereof are identified by row and column.

FIG. 21 is a table showing how the code set up inl the computer output register flip-flops L1 to L6 select the desired character area of the mask.

FIG, 22 shows a portion of the cathode ray tube screen and how an area thereof corresponding positionally to a character area on the mask is scanned by the electron beam.

FIG. 23 is an enlarged view of the portion of the mask of FIG. 20 showing how the horizontal and vertical defiection circuits effect coverage of the character area.

by the cathode ray tube electron beam.

FIG. 24 is an enlarged View of a portion of the mask representing the character area for the character A.

FIG. 25 is an enlarged view of characters as printed on the paper by the system of the invention.

FIG. 26 contains graphs of the phototube output voltage as the character A is scanned.

FIG. 27 is a schematic diagram of the phototube signal shaping circuitry.

FIG. 28 is a schematic diagram of the circuitry for selecting and ydriving the recording bars.

FIG. 29 is a schematic diagram of the circuitry used to energize the paper move relays.

FIG. 30 is a graph depicting the activity of printer components with relation to successive revolutions of the drum.

FIG. 31 shows a schematic view of the dust inker and drier.

FIG. 32 shows the paper take-up mechanism in perspec-` tive.

The printer of the present invention will first be generally described by reference to FIG.' 1, showing an over-A all view of the printer in perspective, with emphasis on the physical arrangement of its component parts. As will be clearly pointed out, the principle employed by the presentinvention to produce visible and legible print at high [speed is basically magnetic, although under electronic control.

lThus codes comprising groups of electrical signals originating from lan external digital source, such as a digital processor, are set up on conductors of cable 103. These coded signals are .transmitted in response to timing signals Cc vgenerated as a result of association between magnetic head 108b and character timing track #2 provided on rotating drum 101. The groups of coded signals are received serially by converter 300 which serves to convert each group to deflection potentials for positioning electron beam 146 of cathode ray tube 132. Converter 300 also provides additional detlection'potentials in `response to timing signals Cs generated by the association of magnetic head 10811 With'the sweep timing track #1. This additional deection causes beam 146 to scan a small area of screen `134 of tube 132. Mask 135, containing a plurality of character-defining areas, one corresponding to each area of screen 134 scannable by beam 146, passes the uninterrupted portion of the illumination caused by thejbeam, onto phototube 139, which converts the modulated light into a series of electrical pulses. Each pulse series thus produced uniquely deines a character.

Converter 300, in its preferred form, is capable of recognizing a maximum of 64 different signal groups from the ysource to Vaccordingly produce 64 different types or kinds of pulse sets or trains. Each pulse train is utilized in recorder 3.01 to energize one or the other of electromagnetic recording heads, designated bar #l and bar #2, positioned adjacent magnetically sensitized paper 114. Selection between bar #l and bar #2 is made in accordance with the positional location on a line of paper 114 to be recorded with the character. Bars #l and #2 are so aligned that the magnetic eld issue therefrom is directed to 'perpendicularly pass through paper 114; and in order to confine the magnetic eld to the position on the line of paper where Vthe character is to be recorded, means are 'provided to concentrate the lield for each character section along a succession of narrow parallel paths ex tending longitudinally on paper 114 a distance approximately equal to the height of the print desired. The means so provided comprises a plurality of magnetically conductive recording projections 107 attached to the surface .of rotating drum 101 along a helical path. Thus, as the drum revolves, these projections successively traverse one of the bars ,#1 or #2 and cause a recording to be made on the paper 114 in accordance with the electrical signal which is energizing the bar at that time. Thus a serial recording of the signals representing each `character section is placed side by side on the same line of paper 114 by successive passes of projections 107 on drum 101. When a complete pulse train is recorded in this fashion, a latent magnetic image of a character is formed .on the paper 114. In order to synchronize the receiving of pulse trains from converter 300* with the passing of the proper prOjections 107 under the bars #l or #2, the start of a printing cycle of the drum is made with reference to timing signals Cg generated by head 108e associated with cycle timing track #3.

During the time that paper 114 is being printed, it is stationarily positioned between drum 101 and bars #l and #2. Upon completion of the printing of one line of sixty characters, paper 114 is moved by action of a pair of relays 120I and continuously rotating shaft 115- so as to be positioned for printing the next line.

Paper 114 is then passed through inker 302 wherein the latent image is made visible. Inker 302 comprises dusting chamber 179 `which receives an air stream by way of duct 18011. 'This air stream was previously mixed with resimcoated magnetizable particles as it passed through reservoir 198; thus, upon expanding in dusting chamber 179, it produces a low velocity cloud 181 of black magnetizable resin-coated particles which surrounds paper 114. A high density of particles is attracted to the surface of paper 114 where the characters have been magnetically formed. The paper is then passed adjacent infra-red lamp drier 182 which employs heat to melt the resin'coating of the particles to a gluelike consistency which, upon cooling, hardens and seals the particles to paper 114, thereby contributing permanence to the characters. Take-up mechanism 202 operates to provide tautness to the paper as it is conveyed through inker 302.V

Having generally described the printer arrangement, reference will now be made to FIG. 2, showing a simplitied block diagram of the functionally prominent electrical circuitry and devices which cooperate to produce the latent character images, together with relevant units of a digital computer, selected as an input device therefor.

The operating system of computer 90, contemplated for use with the preferred embodiment of printer 100 of the presen-t invention, is well known in the art as providing for sequencing through step operations in accordance with a prescribed program of instructions. Step operations in the tiow may be controlled by a program counter 91. This technique conveniently sets up outputs from program counter 91 unique to the program; and, for an instruction which directs transmission of stored information to printer 100, for instance, a step operation may cause the corresponding output of program counter 91 to be conveyed to printer v100 as a star-t signal S on line 93. Start signal S energizes electrical networks in print control circuit 124, which, in turn, activates character counter 125 to count, thereby readying printer components for the receipt of coded information. Selected count outputs from character counter 125 cause transfer circuit 128 `to signal readiness to print by means of a ready signal R sent toy computer by line 94. On receipt of the ready signal R, computer networks control ythe program counter 91 to cause computer 90 to enter a portion of its ow which sequentially resets output register 92 sixty times, each reset in response to an additional ready signal vR sequentially received from transfer circuit 128. Each setting of output register 92 corresponds to a coded information character to be printed on one line of paper 1 14. When the last (60th) character of the line is transmitted and printed, compu-ter 90 may automatically repeat these step operations to provide for printing of further lines. When the computer memory has been depleted of all stored information to be printed at this time, computer 90 enters other portions of its program. Thus it is seen :that character code transmission from computer 90 to printer .is a serial process which is synchronized `by intercommunicating signals S and R.

It has been pointed out that the code corresponding to the next character to be printed is set up by computer 90 in its output register 92, here comprising, in the main, ip-tlops L1 to L6. This code may represent characters of any desired nature: alphabetic, numeric, symbolic, punctuation, ete. In the embodiment to bc described, up to 64 different character codes may be ernployed. The codes `are received by deflection circuits 131 and 136 by way of lines 95 and 96, respectively, and converted to deilection voltages for electron beam 146 of cathode ray tube 132. The deflection voltages direct beam 146 to a location on phosphorescent screen 134 of tube 132 and additional deflection voltages, generated by `deflection circuits 131 and 136 in response to sweep timing signals Cs, cause `beam 146 to repetitively sweep vertically at spaced horizontal positionsto form a raster 133. Beam 146 thus covers a ldifferent rectangular area on screen 134 for each character code. The sweep is fro-m top to bottom of raster 133 and ten successive Y 12 inches in diameter and 12 inches wide.

right in accordance with outputs from sweep counter 126, which generates ten different count outputs To, T1, T9. Positioned adjacent screen 134 such that their surfaces adjoin is a mask 135, opaque over most of its area, but containing translucent portions shaped to conform with up to 64 different characters, which correspond to the 64 different character codes which may be received from computer 90. For each character code received, the area covered by raster 133 conforms to the area of mask 135 which may be occupied by a corresponding character. This arrangement thus causes light to be transmitted through mask 135 as pulses of various durations, .as beam 146 sweeps successive sections of the selected area. The light pulses, which occur in sets of light pulse trains and which deiine the form of the character, impinge on sensitized cathode 141 of phototube 139, `appropriately stationed opposite screen 134. Phototube 139 converts the impinging light energy to corresponding electrica-1 pulse signals which are amplified and shaped by signal shaping circuit 158 and employed to energize one or the other of the magnetic recording bars, designated bar #1 and bar #2, as selected by bar selector circuit 129. Recording means provided by the invention comprise a continuously ro- .tating drum 101 containing the small recording projections 107 of magnetic material arranged in a helical path around the drum circumference. Recording bars #l and #2 are in close proximity to drum 101 such that the direction of bar magnetic flux lines is toward drum 101. Magnetizable paper 114 is intermittently fed, by means of paper move relays 120 as controlled by paper move circuit 157, to pass between the bars and drum 101 Asuch that paper 114 is stationary when bars #1 and #2 are recording, and moving to position a new line for printing after 60 characters have been recorded. Drum recording projections 107 serve as iield concentra/tors to heavilymagnetize paper 114 in lines perpendicular to its surface. The preferred arrangement of recording projections 107 is in groups, each group accomplishing the formation of a single character at a particular area on a line of paper 114. The 60I ycharacters on a line are formed by coincidence of electrical pulses in bars #1 or #2 with the successive traversal of the corresponding recording projections 107 between drum 101 and paper 114. In summary, a magnetic recording of a character is formed at a position on a line on paper 114 by a coincidence of electrical signals in recording bar #l or #2 and the traversal thereunder of the group of iield concentrator projections 107 on drum 101 corresponding to the positional location on the line.

To provide the proper timing intervals for all operations of the printer, the three repetitive clock pulse signals Cs, Cc, and Cg are generated as outputs from shaping circuits 110 from inputs received from magnetic heads 10811, 108i), and 108C sensing the passage of projections 106 arranged on drum 101 in three circumferential tracks, designated the sweep timing track #1, the character timing track #2, and the cycle timing track #3, respectively.

Drum 101, shown in perspective in FIG. 2 and in plan View in FIG. 3, is in constant rotation in the direction `indicated by the arrow on the right end thereof by a motor (not shown) or the equivalent, operating by way of drive 102. Drum 101 is cast of a material, such as aluminum, having properties with little or no effect on magnetic fields, and in the preferred embodiment is about Protruding from circumferential surface 105 of drum 101 are a plurality of projections extending outwardly to a height of approximately 1A; inch. These projections are formed of magnetic material and, in physical configuration, are of two types, as shown in FIG. 4. Each timing projection 106 is similar to a gear tooth, being about lt inch long and positioned, as shown, with the longitudinal dimension perpendicular to the direction of motion of rotating drum 101. l Reference to FIG. 3 will show that 350 timing projections 106 are provided on the rightmost track #1. It is to be noted that the projections 106 in this track are arranged in groups of l0, the projections in each group being evenly spaced. The separation 270 between groups slightly exceeds the separation 271 between projections 106 within a group. Reference to FIG. 3 also shows that 35 timing projections 106 are evenly spaced about central track #2. It is to be noted that the distance 272 between a projection 106 of track #2 and the last preceding projection 106 of a group of track #l is equal to the separation 271 between projections `106 within a Igroup of track #1. Thus a projection 106 of track #2 is displaced a slight distance 273 ahead of the first projection 106 of a group on track #1. Further, it is noted that there is only one projection 106 in track #3 and it is located a slight distance 274 below a projection 106 of track #2. The reasons for this arrangement of projections 106 are reserved for later discussion.

Continuing to regard FIG. 3 in conjunction with FIG. 4, it is seen that recording projections 107, which are cylindrical in elevation, are disposed around the periphery of drum 101 along a helical path. The rightmost portion of the helical path contains 350 recording projections 107; this portion of the helical path is effective during the iirst revolution of the printer cycle. The leftmost portion of the helical path contains 250 recording projections 107. This latter portion of the helical path is effective during the second revolution of the printing cycle. As will be described hereinafter, each printing cycle includes two revolutions of the drum and defines the time during which a line on the paper is printed. In the preferred form, the recording projections 107 are arranged in groups of ten, as shown, each group corresponding to a character to be printed, and each group is laterally displaced from its neighbors by a space 275, as shown. Each group effects the printing of one character and the lateral spacing 275 between groups provides for spacing between characters. The 60 groups effect the printing of 60 characters on one line of paper, the groups being identified in FIG. 3 in accordance with the character designations. It is further noted that each recording projection 107 in the helical path is laterally aligned with one of the timing projections 106 on track #1, and that the last group (corresponding to the 60th character) ends shortof the position of projection 106 of track #3 by a distance equivalent to that required by ten groups. Reasons for this arrangement will be given at a later time.

It may be noted here that, as shown in FIG. 4, in the preferred arrangement, timing projections 106 are formed by an acid etching process on a ferrous metal band 329 which is then forcibly pressed in place over a recessed portion 330 at the right end of drum 101. Recording projections 107 are press fitted into holes 331 appropriately drilled in drum 101.

Returning to FIG. 2, as drum 101 revolves, identical magnetic heads, stationarily positioned close to surface 105, sense the passage of recording projections 106 in each of the tracks. For example, head 108e is thus associated with track #1. As shown in FIG. ,6, head 10811 is of the reluctance type having a permanent magnet 280 withV an air gap 281 containing a pointed stylus 282 on which is wound a coil 283. Head 108a operates such that a change in reluctance of gap 281 due to proximity between the apex of a timing projection 106 and magnet 280 generates an electrical signal in coil 283. The signal is carried by line 109, for the exemplary case, to shaping circuit 110 (FIG. 2) where, as will be shown, it is caused to serve as a basis for 'generating pulses Cs and Cs', employed for timing purposes. Pulses Cc and Cg are similarly generated using the other two tracks #1 and #3, and are also employed for timing Various operations 'of printer 100. It may briefly be noted with reference to these pulses, however, that for each drum revolution,

cycle pulse Cg is generated once, character pulse Cc is generated 35 times, and sweep pulse Cs is generated 350 times; further, that due to the spacing of projections 106 pulse C'g is generated slightly in advance of a pulse Cc and that lpulses Cc are generated slightly in advance of the iirst pulse Cs of a group. It is with reference to these pulses that printer components are synchronized. Thus it follows that sequential operations of printer 100 are in synchronism with drum revolutions.

Also as drum 1111 revolves, the recording projections 107 traverse the area suspended by the pair of positionally fixed, identical magnetic heads, labelled bar #l and bar #2; the projections effective during the iirst revolution of a cycle traverse beneath bar #l and a portion of bar #2, and those effective during the second revolution of a cycle traverse beneath bar #2. These bars, shown in perspective in FIG. 3 |and in cross-section in FIG. 5, are of ferrite material or the like, shaped with a rectangular portion 111 surmounting a triangular portion 112, a. coil 113 being wound on a recess in the former. Apex 153 of triangular portion 112 is ground flat, the width being slightly less than the distance between projections 11317. These bars comprise electromagnets, which, when energized by coil current, due to the orientation of apex 153 of triangular Vportion 112, concentrate their magnetic fields towards surface 165 of drum 101. A more intense concentration of field occurs, of course, in the interstice between apex 153 and therapex of a passing projection y1117. It is this latter concentration of field that contributes to the formation of a character on paper 114. It is noted that, the width of apex 153 being less than the separation between projections 107, only one projection 1417 can be directly below a bar at a time and thus be effective to record. Further, since recording is accomplished by a distortion of iield from a bar by a projection 1117, the width of apex 153, in effect, limits the height of a character. It may falso be noted at this time that a line of 6() characters is printed in -two revolutions of drum 101 on paper 114, stationarily positioned during recording between the bars and surface 105, the first revolution causing the printing of the first through the 35th characters by cooperation of the recording projections 1117 and both bars, and the second revolution causing the printing ofV the 36th through the 60th characters by cooperation of the recording projections 107 and bar #2. It may be pointed out that the second revolution includes a ten character print time delay during which paper 114 may be shifted for printing a next line.

It may be again noted that the last five characters, the 31st to 35th, recorded may be regarded as an overlap. It has been determined that the field resulting from electrical energization in a bar extends beyond the area of the'bar and, particularly, into the area of the other bar a distance of approximately lthirty times the distance between recording projections 107. Thus, regarding FIG. 3, if the right end of bar #2 were to be traversed by recording projections 107 during the recording of the 1st, 2nd, and 3rd characters, the eld of bar #l extending below bar #2 would produce a duplicate recording of these characters at the area of paper later to be recorded by energizing bar #2 at Ithe beginning of the second revolution of the printing cycle. The overlap provides lateral displacement at the right end of bar #2 of 50 times the lateral distance between recording projections 107 at .the right end of bar #2. Thus, during the recording of the first three characters by bar #1, bar #2, not having eld concentrators to cooperate therewith, produces no recording.

-It has been pointed out in connection with'a discussion of drum 1111 that three independent clock signals, designated C5, Cc, and CE, of pulse form, are generated by shaping circuits 111B employing the output of heads ltia, liib, and 108e (FIG. 2). Shaping circuits 110 are identical and will now be described with reference 8 to that shown in FIG. 6, which generates pulses C, and C As a timing projection moves past head 108a, electrical pulse 161i 'appears on line 169, by which the head is coupled to two-stage amplifier 164. The output of amplifier 164 comprises pulse 169, a magnied iii-phase replica of pulse 163, and is fed to trigger circuit 165, comprising tubes 17h and 171. Normally, due tothe grid biasing arrangement and common cathode resistor 172, tube 170 is cut off and tube 171 is conducting heavily. Pulse 169, being positive with reference tothe ground return of tube 170, at some point of its leading edge, causes tube 170 to start conducting. The resulting decrease in plate potential of tube 170 is impress-eden the grid of tube 171 through network 332, and theY increased voltage drop across common cathode resistor 172 causes a steep rise in the plate potential of tube 171.

This condition is maintained while the amplitude of pulse Y 169 is more positive than lthe potential that caused the condition.

Similarly, the conduction in tube 170 is sharplycut off at a point on the trailing edge of pulse 169. Thus the output of trigger circuit 165 is squared pulse 173 having a time duration approximately equal to that between triggering amplitudes of pulse `169. Pulse 17,3 is coupled to one-shot 166, which, being in a condition such that tube 1741 is normally cut off and tube 17'5 is normally conducting, produces in this case a pulse output corresponding to the leading edge only of pulse 173. ri`he output, pulse 176, isvin phase with pulse 173 and, as is well known, has a duration as established by the time constant of the one-shot circuitry, here approximately 5 microseconds. `Pulse 176 is conveyed to twostage driver-amplier 167, where it is amplified, inverted, and clamped between the potentials +100 v. and -l25 v. to give the output pulse CS which, in tube 178, is also amplified, inverted, rand clamped between +100 v. and v. to give the output pulse Cs.

lt has been pointed out that the other clock signal pulses Cg and Cc are also generated in this manner. It will be noted from yFIG. 2, however, that the primesof these pulses are not employed.

As shown in FG. 2, two binary counters are embodied in the printer, character counter 125 and sweep counter 126, the former producing 61 discrete outputs and the latter producing 10 discrete outputs. nThe means `ein'- ployed in the counters to 'produce these outputs are well understood in the 'art and will Vbe but briefly presented here.

1t has been indicated that selected `count outputs from character counter 125 cause a signal R, signifying that the printer is ready to receive a character code, to be transmitted to the computer. More broadly, a-s will be made apparent, this counter establishes time intervals for all operations of printer 111). v

Character counter 125 is shown in block form in FIG. 7 to comprise seven flip-Hop circuits, A1 to A7, coacting by virtue of diode network 127 to produce 61 outputs, S0 to S59 and SX. The count output of character counter 125 is arranged to change on receipt of input pulse NlC,J from print control circuit 124 (FIG. 2). With momentary reference to FIG. 3, it may be noted that the outputs S0 S3., occur during the first revolution of a Vprinting cycle as the first 35 characters are beingV printed,V

the outputs S35 S59 occur during the second revolution of a printing cycle as the remaining 25 characters are being printed Yand the output Sx occurring at all other times, i.e., during the ten character-time hiatus Yreserved for shift-ing paper 114 from printing the next line V(following the count S59) and during quie'scence as defined hereinafter. Selected outputs from character` counterV 125 are fed as inputs to print 'control circuit 124, transfer circuit 123, and bar selector circuit 129, to be discussed later.

Referring again to FIG. 2, sweep counter 4-126 foperates through its counting cycle as the group of 10 projections 107 corresponding -to a character traverses past bar #1 or bar #2. The outputs lfrom sweep counter 126 are fed to horizontal deflection circuit i131 wherein they act to position electron beam 146 of cathode ray tube 132 to permit scanning of successive sections of raster 133. Sweep counter 126 is shown in block -form in FIG. 8 to comprise four iiip-op circuits, B1 to B4, coacting by virtue of diode network 130 to produce 10 sequential output counts To, T1 T9, respectively, the output being arranged to change on receipt of successive pulses Cs.

Table I summarizes the activity of sweep counter 126. It may be observed that the output counts have been selected with regard to symmetry of the states of the llipops in combination. The reasons for this type of selection will be made apparent in connection with a discussion of horizontal deection circuit 131.

TABLE I Sweep counter 126 Flip-Flops Sequential Count Designation B1 B2 B3 B4 Still with reference to FIG. 2, it is seen that intercommunication between computer 90 and printer 100 components is by lines 93, 94, 95, and 96 carrying three types of signal.

The first of these signals is start pulse S, on line 93, which is generated as an output count of program counter 91 when the iirst operation in the program read out to printer is accomplished, and is received by print control circuit 124. Print control circuit 124 is energized by the start pulse S to cause character counter 125 to change its output from the static count Sx and sequence through its count cycle. The outputs S to S58 and Sx of character counter 125 are conveyed to transfer circuit 128 wherein they are logically multiplied by output N1 of flip-flop N1 and pulses Cc. The resulting signal, designated for simplicity as pulse R, is sequentially transmitted by line 94 to program counter 91, and is effective to advance the program whereby output register 92, comprised mainly of Hip-flops L1 to L6, is sequentially set up with codes representing characters for which printing is to be done. Thus it is noted that ip-ilops L1 to L6 are reset with a new character code only in response to receipt by program counter l91 of a pulse R, transmitted by transfer circuit 128 only when printer 100 is [ready therefor, as for instance, after the printing of a prior character has been completed. For the printing of one line of -60 characters, sixty R pulses are transmitted. The pulse Cc, after the transmission of the last pulse R, is identified by -print control circuit 124 which acts to stop the printing process and energize paper move circuit 157 to cause paper 114 to be shifted ahead for printing of the next line. The last pulse R is also identitiied by program counter 91 which acts to cause computer 90 to re-enter the `first operation in the program read out -to printer if additional character codes are available in the computer memory, or, otherwise, to enter a routine in the program which identities the next command to be executed.

The third type of signal, transmitted on lines 95 and 96 from output register 92 on receipt of pulse -R from transfer circuit 128, comprises the binary code representing information Stored in the computer memory. Up to `64 codes can be handled in the preferred embodiment of the invention. In response to each pulse R that is received, computer sets up ilip-iiops L1 to L6 to represent the code of a character. Thus the 12 output lines from ilip-ilops L1 to L6, labelled in FIG. 2 as L1, L1', L2, L2', Le, L6', in combination, represent the code ot a character. Six of the lines, combined as line 96, are energized by the outputs from flip-flops L1, L2, and L3, and are received by vertical deflection circuit 136. Six of the lines, combined as line 95, are energized by the outputs from flip-flops L4, L5, and L6, and are received by horizontal deection circuit 131. Deflection circuits 1311 and 136 operate to deflect electron beam 146 of cathode ray tube 132 to impinge on tube screen 134 at the area, one of the 6-4 character areas, determined by the code presently set up in flip-flops L1 to L6, and, additionally, provide deection voltages comprising l0 different horizontally deecting potentials and l0 vertically deflecting sweep potentials, respectively. The states of flip-ilops L1 to L6, presented in FIG. 2l, will be shown to select a character area of mask 135 by row and column, in connection with a discussion of that iigure hereinafter.

The present printer employs the ip-flop type of bistable state circuit for control of various of its ope-rations, the ilip-iiops being designated as follows:

Flip-flop Q1 denes the time interval between receipt of start pulse S from computer 90 and the printing of the last character of a line.

Flip-flop N1 defines the two revolutions of drum 101 which comprise the printing cycle.

Flip-Hop M1 controls switching between the two recording bars #l `and #2.

Flip-flop P1 controls the enerigization to paper move relays 120.

Flip-Hops A1 to A7, inclusive, function, as shown rin connection with FIG. 7, `as binary stages vfor character counter 125.

Flip-flops B1 to B4, inclusive, function, as shown in connection with FIG. 8 vand Table I, as binary stage for sweep counter I126.

The nomenclature used to express terms of logical equations which are employed to describe the -activity of circuitry will next be outlined. Terms in such equations lare generally based on the states assumed by bistable circuits having two inputs and two outputs, `such -as flip-Hops, the outputs being clamped at the preferred logical potentials of +125 v. and +100 v. These circuits will have designations comprising a letter-number combination. lFor example, -flip-ilop N1 is triggered into a true state, i.e., output N1 is at +125 v., by an -input n1; and into a false state, i.e., output N1 is at +125 v., by an input 0n1. When one output of the circuit Iis at +125 v., the other output is at v. Networks are arranged to respond to these voltages, which may thus be considered to represent the binary values one and zero, respectively.

As shown -in lFIG. 9, a schematic diagram of the preferred form of flip-op, here designated ip-llop N1, the circuit Iincludes tubes 234 and 235 intercoupled by networks such yas network 237. In eac-h tube, the plate is connected to a +225 v. supply through a resistor such V'as resistor 238; the grid is connected to a -300 v. supply through a resistor such as resistor 239, and the cathode is grounded. Inputs @n1 and n1 to the grids of tubes 234 and 235 -are from and gates 240 and 241, respectively, and are differentiated by networks such las network 242 and clipped `at the +3 v. level Iby diodes such as diode 243. Thus only negative pulses are eiective on the grids. For each tube, also, the plate is clamped at the potentials +100 v. and +125 v. by diodes such as diodes 244 and 245.

Assuming that dip-flop N1 is false, i.e., output N1' is at v. `and output N1 is at +100l v., la negative pulse Ymence counting through itscycle.

'applied to'the grid of tube235'will1cut this tube ofi, there- 'lbycausingoutputlNl' todropto +1.00 v. and output N1 `r`toirise to +125 v. This'fpulse -is providedbyfoutput n1 from and l gate 241, occurring when all #of the inputs -N1 Q1, M1', and Cg are at +125 lv..and'pulse.Cg abruptly l' l-falls `to +100 v. -The differentiation of 'the fall produces pulse which acts as the requisite negative-going trigger. -Thus, the equation ffortrigg'ering tlip-op-NI truernay be written, in logical product `for1n,in accordance with well-known principles of vBoolean algebra, as

n1=N.1'Q1M1'Cf,r

`'andisshowrn together 'with the Onl equation, below the circuit.

The curves Vof FIG. 13 illustrate the tniggering of flip- `iiop N1 in accordance with the n1 equation. Line I repre- -sentspuls'e MlCg, which, it will be recalled, occurs-once -for each revolution `of drum 101 and is the output of the logical and.gate `shown in FIG. 15. Line IIsho-ws output Q1 of Hip-flop Q1, which, in laccordance with the n1 equation, is `required to be at-+l25 v. in order that -llip-liopvNlimay-be triggered true. yIt will be shown-that `iiip-iiop-Qlrlisset true by startipulse S Areceived from the computer, in this case at -a time prior to thegenerav"tionof a pulse CE, and that, for'this condition, flip-flop -Mlris false, thereby making bar #l available for recording. Thus and'gat`e 241 (FIG. 9) is arranged to make v'the true input of iiip-llop N1 Vresponsive 'to yCg trigger pulsesprovided'the iiip-iiop is in the falsestate. In line III this latter provision is shown to be met. -It is thus ythe pulse 1M1Cg that determines when an effective true input n1 (-line IV) will be generated. However, flip- Aliop lN1 will be triggered true only by ya negative-going pulse applied to its true grid. This pulse occurs, as shown fin -line fV, :when input n1 sharply drops to a low potential at the `fall of pulse MlCg. Thus, as line VI shows, outputNl'swings to +125 v.

lFor-'otherbistable circuits, resortwill be rmade to block diagrams to represent the schematic form, as illustrated in-FIGS. 10,111, and l2 for ip-tlops P1, Q1, and M1, and lthe :Boolean equations and networks which `define when and 4how the circuit is to change will be shown f therewith.

Logical 'sum` networks, such as or gate 246 `of FIG. 12,are also well known -to ope-rate to produce lan output,

-in thiscase of +125 v. .on Iline 247, when at least one of theY inputs, Vhere terms N1 and S59, is' at +125 v., otherwise the output'on line 247 is at +100 v. The output of or gate 246 vmay thus be represented as a logical sum term(N1'-+S59), which is seen to be an input to an and network-248, where the logical product (N 'fi-559)@ is generated,'thus forming input ml to ip-op M1.

It will berecal-led from FIG. 2 that print control circuit 124 operates, on receipt-of a start-pulse S from the computer, to produce a series of `pulses NlCc which is' fed to character counter 125, which, in turn, responds by changingits output-from quiescent count SX to .com-

Print control circuit 124-vcomprises flip-flops N1, P1, 'andfQl and their associated triggering networks shown in FIGS. 9 Ito l1, inclusive,- and the network shown in FIG. 14.

-From'FlG 1l, the-equation q1=S indicates that flipflop Q1 isset true b-y -a start pulse S, emitted by computer 90 on entering itsV printroutine. It will become app-arent :in `the following `discussion that, as long as this tiip-op remains false, printing is.not.done. Thusprinter 100 may lbeconsidered to-be .quiescent when flip-flop Q1 is in the :.falsestate. The equationy q1 =S59Ccoperates to set iiipl1 flop Ql-false when the last character lof alineis printed, `thereby returning theprin-ter to the quiescent state.

The equations 0n1=N1Q1M1C8 and n1=N1Q1M1Cg ofFlG. 9. indicate'that the state of ip-ilop N1 is determinedby the state of flip-dop Q1 at thefall of a pulse Cg,

which, it'will .be recalled, isgenerated once eachrevolution of drum 1011. Output M1' of hip-flop M'Iappears Vrevolutions of drum 101.

Referring now to FIG. .14, the true output N1 ofiflipilop N1 is seen to be combined in an and gate with pulse CC to form the logical product NiCc, representing a pulse which is generated 35 times for each revolution of drum 101. These pulses arefed to character counter 125 (FIG. 2), which is triggered thereby to 'produceits cyclical output counts.

As indicatedV in connection with FIG. 2, transfer circuit 128 emits the pulse R online 94 informing vcomputer 90 that printer is ready to receive the next character code, and thus causes flip-flops Llvto L6 to be reset. The circuit is shown in FIG. 17 to comprise logical "orgate 290 which sums the selected outputs S0, S1, S58, Sx of character counter to form the` term Sa; yand logical and circuit 29'1 in FIG. 16 which generates signal pulses: R=SN1Cc. The selected outputsof character counter 125 used to Aform term S,l will befurtherdiscussed with reference to FIG. V30, and it will be shown that' the selected outputsare individually effective totime the transmission of a pulse R to computer 91).

The action of deflection circuits 131 and-136 willnext "be discussed.

With reference to FIG. 2, both deection circuits-generate voltages `which affect beam 1460i tube 132 at the position on screen 134 determined inthe vertical direction vby the setting of liip-liops L1 to L3 and in the hori-` zontal directionl by the setting of Hip-flops L4 to L6.

Vertical deflection circuit 136 generatesten linear-vertical sweep voltages'for beam 146, one to correspond to each of theten Cs pulsesreceived during the timewlren the ten projections `107 corresponding to a character are traversing recording bar #l or #2. The sweep voltages are of equal amplitude and period and, as shownin the enlargement of a portion of screen 134 of FIG. 23, `the beam traces which they produce are displaced from each other an incremental distance as determined by horizontal displacement voltages generated by horizontal dciiection circuit-131.

Returning to FIG. 2, horizontal deection circuit 131 generates ten incremental displacement voltages for beam 146, one to correspond to each `of the ten count outputs To to T9, receivedfrom sweep counter 126. These :voltages are D.C. and operate to position sweeps `generated by vertical deflection circuit 136 small incremental horizontaldistances such thatfthe rstsweep (see FIG. 23) generated'fora character is positioned near the left side of the character-area, the second is positioned to` the'right of therst, etc.,'the tenth sweep being positioned near the right side of the character area.

Screen 134 may be considered to be divided so.as\to accommodatefin its centralportion, a square raster cornprised of -64 smaller-characteriarea rasters 133. For convenience, character area rasters 133 may be laid out in an eight .by` eight matrix, the columns corresponding to vertical deflection of beam 146 and the rows corresponding.

to horizontal deectionof beam 146, Vand may be referenced to mask 13S shown'in FIG. 20'. It follows thato'ut- .put from verticaldeflection circuit 136 (FIG...2) will position beam '146 Iat `a row (FIG.'20) and that theoutput lfromhorzontal deflection circuit 131 will position beam 146 atacolumn (FIG. 20). Thus bearn146-will be positioned to a particular character area, the selection being a function of the states of flip-flops L1 to L6. The selection is illustrated in FIG. 2l, whereit isseen that, since flip-flops L1v -to L3'feed into vertical deflection circuiti-136, 

